More than 16 million people in the United States are afflicted with diabetes mellitus or have a predisposition to diabetes, and more than 750 thousand people are registered annually as diabetics. The medical complications associated with diabetes are quite serious, including increased risk of kidney, eye, nerve, and heart disease. To control their condition, diabetics must control their blood sugar levels by selecting proper nutrition and, in the more serious Type I condition, by administering insulin. To help guide their nutrition and their regimen of insulin injections, diabetics must also measure their sugar levels several times a day.
At present, all portable devices for measuring blood sugar require puncturing the fingertip to obtain a blood sample. The blood sample is then placed on a test strip that indicates the glucose concentration. An example is the ONE TOUCH.RTM. glucose meter sold by the LifeScan Co. These devices are very compact and reasonably accurate, but puncturing the fingertip to obtain a blood sample is inconvenient and painful and poses a risk of infection. No commercial alternatives are available.
A number of attempts have been made to measure blood sugar concentration noninvasively by measuring tissue absorption of light radiation in the near infrared energy spectrum--approximately 650 nm to 2700 nm. Various attempts are described in U.S. Pat. No. 4,655,225 (Dahne), U.S. Pat. No. 5,070,874 (Barnes), U.S. Pat. No. 5,077,476 (Rosenthal), U.S. Pat. No. 5,086,229 (Rosenthal), U.S. Pat. 5,277,181 (Mendelson), U.S. Pat. No. 5,361,758 (Hall), U.S. Pat. No. 5,459,317 (Small), and U.S. Pat. No. 5,529,755 (Higashio).
Some of these prior patents, such as U.S. Pat. Nos. 5,070,874, 5,077,476, and 5,086,229, disclose only using wavelengths less than 2000 nm, most of which do not penetrate well through human skin. Others of these patents, such as U.S. Pat. Nos. 4,655,225, 5,277,181, 5,361,758, 5,459,317, and 5,529,755, disclose applying multiple wavelengths of energy and require complicated apparatus, such as a continuous wide-band radiation source, which restricts the ability to construct a compact portable unit from these designs.
U.S. Pat. No. 5,313,941 (Braig) discloses using a radiation source of long infrared energy, specifically from 2000-20,000 nm, applied in short bursts to avoid patient discomfort and/or burning of tissue. In a preferred embodiment, a wavelength of approximately 9100 nm is used to detect the concentration of glucose, and a wavelength of approximately 10,500 nm is used as a reference. The source of infrared energy is a heating element that radiates a broad spectrum of energy, and a mechanical shutter regulates the flow of energy into short bursts. In addition, the mechanical shutter is synchronized with the patient's systolic and diastolic phases of the cardiac cycle. A disadvantage of this method is that sophisticated filters and photodetectors are needed to measure the signals in these spectral regions. Another disadvantage is that the high energy source requires a large power supply, which restricts the ability to construct a compact and portable unit.
U.S. Pat. Nos. 5,398,681 and 5,448,992 describe a polarizing method to measure blood sugar concentrations. Disadvantages of these methods include but are not limited to the need for many elements, fine adjustments, and precise techniques to fix changes in the plane of polarization when measuring blood-sugar/glucose concentrations. Another disadvantage is that the negative influence of other blood constituents is not excluded in the measurements. An apparatus of this nature could not be constructed to form a compact and portable unit.
In short, to date, all attempts have failed to replace the current methods of measuring blood glucose concentration with a noninvasive glucose analyzer that is accurate, convenient, portable, and reliable.